docs(ci): ADR-ci-003 — cross-platform release builds (D1 matrix)
Record the multi-platform build strategy as its own decision: cargo-zigbuild for the four non-macOS targets, the static/standalone posture per platform, the Windows synchronization stub, the test->build matrix workflow, and the macOS deferral with its licensing rationale (the public CI image can't carry the SDK). Shrinks the ci-001 amendment to a pointer; updates the index. Runtime-verified by the user: Linux x86_64 + Windows aarch64 run correctly.
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# ADR-ci-003: Cross-platform release builds (the D1 matrix)
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## Status
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**Accepted (2026-06-13); implemented the same day on the `ci` branch.** Every
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fork was settled with the user. Verified end-to-end:
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- all four targets cross-build locally from Linux x86_64;
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- the Linux binaries are statically linked (D2); the Windows artifacts are
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valid PE32+ (x86-64 / Aarch64);
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- a real release-matrix run (tag `v.0.0.0-citest3`) published **8 assets** — the
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four binaries + a `.sha256` each.
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**Runtime-verified (2026-06-13, by the user):** the **Linux x86_64** and
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**Windows aarch64** binaries launch and run correctly — one of each OS family
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and both architectures. The remaining two (**Linux aarch64**, **Windows
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x86_64**) are link-clean and valid format but not yet runtime smoke-tested.
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This ADR records the **cross-platform build strategy**; it sits on top of
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**ADR-ci-002** (the nix flake, which now carries the cross toolchain) and
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**ADR-ci-001** (the pipeline, whose release job this fills in).
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## Context
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`requirements.md` **D1** asks for binaries on **Linux, macOS, Windows × x86_64
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and aarch64** (six targets); **D2** asks for a **single static binary, no
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runtime deps**. The CI runner executes jobs in a **Linux x86_64** container
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(ADR-ci-001), so every target is **cross-compiled from Linux**.
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What's feasible is decided almost entirely by one dependency — **`arboard`**
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(the clipboard backend for the `copy` command). Its per-platform backends in
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`Cargo.lock`:
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| Target family | arboard backend | Needs a platform SDK to cross-link? |
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|---|---|---|
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| Linux x86_64 / aarch64 | `x11rb` (pure Rust) | No |
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| Windows x86_64 / aarch64 | `clipboard-win` + `windows-sys` (import libs bundled) | No |
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| **macOS x86_64 / aarch64** | **`objc2-app-kit` → links AppKit** | **Yes — Apple's SDK** |
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So **four targets cross-compile with no SDK**; **macOS is the hard wall** —
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AppKit can only be linked against Apple's SDK.
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## Decision
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### 1. Tooling — `cargo-zigbuild`
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Cross-compile with **`cargo-zigbuild`** (Zig's bundled clang + libc as a single
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universal cross `cc`/linker), added to the flake devShell alongside `zig`. One
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tool serves every non-macOS target, **including the `cc`-crate compile of
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rusqlite's bundled SQLite C**, with no per-target toolchain. It replaced the
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earlier single-target musl `cc` (ADR-ci-002's first cut).
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### 2. Targets this iteration — the four non-macOS
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Added to `rust-toolchain.toml` and the release matrix:
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- **`x86_64-unknown-linux-musl`**, **`aarch64-unknown-linux-musl`** — musl +
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`crt-static`, so **fully static** portable binaries (D2);
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- **`x86_64-pc-windows-gnu`**, **`aarch64-pc-windows-gnullvm`** — Zig statically
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links its libc, so the `.exe` is **standalone** (no mingw runtime DLLs).
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### 3. The Windows `synchronization` stub
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Rust's `std` links **`-lsynchronization`** (its `WaitOnAddress`-based thread
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parking). That import library is normally supplied by Rust's `rust-mingw`
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"self-contained" component — which **rust-overlay does not ship** — and Zig's
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mingw doesn't carry it either, so the link fails with *"unable to find dynamic
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system library 'synchronization'"*. The functions (`WaitOnAddress`,
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`WakeByAddress*`) are **forwarded by `kernel32`** (already linked), so an
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**empty stub** `libsynchronization.a` (committed at **`ci/winstub/`**, 8 bytes,
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wired via **`.cargo/config.toml`** for the Windows targets *only*) satisfies the
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linker without contributing symbols. Host and Linux builds are untouched by it.
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### 4. Workflow shape — test once, then a build matrix
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`release.yaml` is **`test` → `build`**:
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- **`test`** runs once on the host (`cargo test`) — a tag never publishes
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untested code;
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- **`build`** is a **matrix over the four targets** (`needs: test`,
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`fail-fast: false`), each `cargo zigbuild --release --target <triple>`, then
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packages the binary (`.exe` for Windows) + a `.sha256` and uploads both to the
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**shared release** via an **idempotent create-or-get** (the first matrix job
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creates the release; the rest fetch it).
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### 5. macOS — deferred, with rationale
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macOS is **not** in this iteration. `arboard`→AppKit needs the macOS SDK, and:
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- the SDK ships **only inside Xcode**; Apple's license ties its use to
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**Apple-branded hardware**, so using it on a Linux runner is a **grey area**
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(widely done, low enforcement, but technically against the terms);
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- **redistributing** the SDK is a clearer violation — and our **CI image is
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public**, so the SDK **cannot be baked into it** even if the grey area were
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accepted; it would have to live in a private store;
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- the **clean** path is building on **real Apple hardware** (a Mac registered as
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a Gitea runner, or hosted Mac CI), where the SDK is fully licensed.
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macOS therefore becomes its **own step**, choosing between **(a)** osxcross + a
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**private** SDK kept out of the public image, or **(b)** a **Mac runner**. The
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user decides when we get there.
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## Consequences
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- **D1: four of six targets met** from a single Linux runner; **D2 met on
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Linux** (static musl). Windows `.exe`s are standalone.
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- **Runtime coverage:** Linux x86_64 + Windows aarch64 confirmed running
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(user, 2026-06-13); Linux aarch64 + Windows x86_64 are the outstanding
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runtime checks.
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- **Each matrix target recompiles from scratch** (~2–4 min; ~10 min total on the
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single runner), and Zig's per-target libc cache is cold each run. Fine at
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release frequency; cacheable later if it matters.
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- **The empty stub depends on `kernel32` forwarding `WaitOnAddress`** (true on
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Windows 8+), which covers every supported target.
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- **Asset naming** `rdbms-playground-<tag>-<target>[.exe]` is close to what
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`cargo-binstall` / the D3 package managers will want.
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## Alternatives considered
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- **`cross` (cross-rs).** Docker-image-per-target; covers Linux + Windows but
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**not macOS** (no legally redistributable Apple images), and needs DinD
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orchestration inside our job. Rejected — no macOS, more moving parts than
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zigbuild.
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- **Per-target nix cross (`pkgsCross`).** Clean for Linux-musl and
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Windows-x86_64 (mingw-w64, which *does* ship `libsynchronization.a`), but
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Windows-aarch64 isn't readily packaged and **macOS-from-Linux is unsupported**
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in nixpkgs. Rejected — incomplete.
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- **Native runners per OS.** Cleanest for macOS/Windows, but needs mac/windows
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runners we don't have. Kept on the table specifically for the deferred macOS
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step.
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- **A real `libsynchronization.a`** (from nixpkgs mingw or a `rust-mingw`
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component) instead of the empty stub. More principled, but more flake
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machinery, doesn't cover Windows-aarch64, and unnecessary — the stub links
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clean because the symbols resolve via `kernel32`.
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## Deferred / out of scope
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- **macOS** (x86_64 + aarch64) — the SDK/runner decision above.
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- **D3 packaging** — Homebrew / Scoop / winget / `cargo-binstall` manifests
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(and binstall-friendly archive naming).
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- **CI speed** — caching per-target builds / Zig's libc cache.
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- **Runtime smoke test** of the two not-yet-checked targets (Linux aarch64,
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Windows x86_64).
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## Relationship to other decisions
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- **Extends ADR-ci-002** — the flake devShell now carries `cargo-zigbuild` +
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`zig` and the four release targets.
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- **Fills in ADR-ci-001 §3 (Release)** — that single-target job is now this
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matrix.
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- **Advances `requirements.md`** **D1** (4/6) and **D2** (Linux, done).
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